X-ray devices used in the medical field contain an X-ray tube which typically includes a cathode which is heated to emit electrons, a (typically rotating) anode having a target surface facing the cathode, and a surrounding glass and/or metal frame containing an X-ray-transparent window secured by a window mount. Some emitted electrons strike the target surface and produce X-rays, and some of the X-rays exit the frame as an X-ray beam through the X-ray-transparent window. Other emitted electrons do not produce X-rays and are backscattered when they strike the target surface. Many of the backscattered electrons go on to strike and heat the frame including the X-ray-transparent window and the window mount. The frame is also heated from within by other sources such as thermal radiation. The heated frame is typically cooled by a liquid coolant, such as oil or water, located between the frame and a surrounding casing.
The heating of the frame is uneven and often has a peak in the region of the X-ray-transparent window due to the backscattered electrons concentrated there. The dissimilar coefficients of thermal expansion of the X-ray-transparent window and the window mount generate mechanical stresses which can cause tube failure. Additionally, high temperatures in the X-ray-transparent window itself can induce boiling of the adjoining liquid coolant. Such coolant boiling will degrade the quality of the X-ray beam which exits the frame through the X-ray-transparent window. Existing grounded metal frame tubes include those having high-cost components to mechanically join the window to the rest of the frame while reducing thermal stresses to acceptable levels. Some known tubes have enhanced cooling applied to the window region.
What is needed is an improved X-ray tube design which reduces heating of the X-ray-transparent window and the window mount.